You can associate Classic Load Balancer (CLB) instances with a scaling group. CLB instances are formerly known as Server Load Balancer (SLB) instances. The CLB instances distribute traffic to multiple Elastic Compute Service (ECS) instances in the scaling group. This improves the performance of the scaling group.


  • You have one or more CLB instances in the Active state. For more information, see Create a CLB instance.
  • The CLB instance and the scaling group reside in the same region.
  • The CLB instance and the scaling group are in the same virtual private cloud (VPC) if their network type is VPC.
  • If the network type of the CLB instance is classic network, the network type of the scaling group is VPC, and the backend server group of the CLB instance contains ECS instances of the VPC type, the ECS instances and the scaling group must be in the same VPC.
  • At least one listener is configured on the CLB instance. For more information, see Listener overview.
  • Health check is enabled for the CLB instance. For more information, see Configure health check.

Background information

CLB allows multiple ECS instances in a region to share the service load by configuring the IP address of a CLB instance. These ECS instances act as a high-performance and high-availability application service pool. CLB distributes and controls traffic by using CLB instances, listeners, and backend servers. For more information, see What is CLB?.

After a CLB instance is associated with a scaling group, all ECS instances, including automatically and manually created instances in the scaling group are added to the backend server group of the CLB instance. The CLB instance distributes traffic to the ECS instances based on traffic distribution policies and health check policies. This improves resource availability.
Note Each ECS instance in the backend server group of an CLB instance has a default weight of 50. You can adjust the weight of an ECS instance. For more information, see Change the weight of a backend server.


The following section describes the procedure to associate a CLB instance with a scaling group in the Auto Scaling console. For information about other parameters, see Create a scaling group.

  1. Log on to the Auto Scaling console.
  2. In the left-side navigation pane, click Scaling Groups.
  3. In the top navigation bar, select a region.
  4. Go to the page on which you can associate CLB instances with a scaling group.
    • To create a scaling group to associate with CLB instances, click Create.
    • To modify a scaling group that is not associated with CLB instances, find the scaling group and click Edit in the Actions column.
  5. Specify Network Type if you are creating a scaling group.
  6. Specify Associate CLB (Formerly Known as SLB) Instance.
    1. Select a CLB instance.

      By default, you can associate a maximum of 30 CLB instances and five vServer groups with a scaling group. To manually apply for a quota increase, go to the Quota Center. If no CLB instance is available in the drop-down list, check whether your CLB instance meets the prerequisites.

    2. Select backend server groups of the CLB instance.

      You can select default server groups and vServer groups for a scaling group. For more information, see Overview.

      • Default server groups contain the ECS instances that receive requests forwarded by a listener. If no vServer group or primary and secondary server group is specified for listeners, the listeners forward all requests to the ECS instances in default server groups.
      • You can select vServer groups if you want to forward requests to different backend servers, or forward requests based on domain names or URLs.
  7. Configure the remaining settings.